Sewage effluent, industrial pollutants, surface runoff, animal waste and carcasses impact the potability of water worldwide. In many parts of the world, bacteria, protozoa, and/or parasites also impact the potability of water-particularly significant pathogens including: Giardia lamblia, a flagellated protozoan parasite, and Cryptosporidium, a genus of protozoan, which commonly cause diarrhea. To address such pollutants and pathogens, the sterilization of water is a critical need. Common methods such as filtering or boiling water may not be fully effective. Filtering can remove most bacteria and protozoa, but not viruses. Bacteria form spores that are resistant to boiling. Further, some strains of bacteria are resistant to heat above the boiling temperature of water.
Alternative chemical means of purification, such as the use, for example, of chlorine, chlorine dioxide, silver ion/chlorine dioxide, sodium hypochlorite (bleach), iodine, or ozone, can be hazardous—as such materials themselves are potentially hazardous to the user and the environment. Further, neither chlorine nor iodine alone is considered completely effective against Cryptosporidium, although they are partially effective against Giardia. Other known chemical means, such as the use of bromine ion exchange resins and granular calcium hypochlorite are generally not effective in killing highly resistant microorganisms.
Further, alternative means of water purification involve electrochemical sterilization, such as disclosed in U.S. Pat. Nos. 4,236,992, 4,308,117, 4,555,323, and 4,761,208, which means the use of electrodes and/or electrolytic cells. Electrochemical methods, as disclosed in these patents, require a power source, are relatively expensive while using and discharging materials which are potentially hazardous. The requirement of a power source is particularly restrictive.
Finally, an alternative nonchemical mean, such as the use of ultraviolet radiation is not effective in turbid water, and not very effective against viruses. Also, the use of relatively low intensity natural sun light UVA radiation can take significant time to produce the desired sterilization, and the use of relatively more intense artificial ultraviolet radiation can be potentially harmful to the user and also requires a power source and relatively significant cost.
As stated above, ozone (O3, also known as trioxygen) is one of the alternative chemical means of purification, functioning as a powerful oxidant; however, O3 is known to damage mucus and respiratory tissues in animals, and to damage plant tissues. Another form of oxygen is singlet oxygen (or 1O2) which is less stable than triplet oxygen, the O2 present in air, lasting only a about an hour at room temperature—depending on the local environment—so as not to be as environmentally damaging as ozone. Singlet oxygen is a very reactive oxidant, which is known as a means of killing cancer cells in photodynamic therapy. Also, work by P. Wentworth, Jr., et al, Science (2002) 298, 2195, indicates that singlet oxygen might form in aqueous biological environments dihydrogen trioxide (HOOOH), a powerful oxidant that antibodies might use to destroy bacteria. Interestingly, further, Maria C. DeRosa, et al, in an article titled: Photosensitized singlet oxygen and its applications, Coordination Chemistry Reviews, 233-234 (2002), pgs. 351-371, reported that significant work has been done on the use of photosensitized singlet oxygen in oxidation reactions for use in wastewater treatment. For example, with respect to use of photosensitized singlet oxygen for the conversion of sulfide to sulfate in aqueous solution—a reaction which is important in wastewater treatment—DeRosa reported on the use of Al(III), Zn(II), and Ga(III) complexes of anionic 2,9,16,23-tetrasulfophthaloxyanine, with the addition of oppositely, i.e. positively charged detergents to discourage aggregation; especially, Zn(II) phthalocyanine; Zn(II)-2,9,16,23-phthalocyanine tetracarboxylic acid; and/or sulfated phthalocyanine. DeRosa concluded that Zinc phthalocyanines showed oxygen consumption consistent with the complete conversion of sulfide to sulfate in aqueous solutions (and photosensitized singlet oxygen was thought to be responsible for the photooxidation). DeRosa opined that, once again, the use of detergents, such as cetyl trimethyl ammonium chloride (CTAC) strongly enhances the photoactivity of the sensitizers that have high aggregation tendencies—such as the subject phthalocyanines—and that detergents are required to avoid such aggregation that reduces reactivity. However, detergents such as CTAC are known to be very toxic to aquatic organisms, to be harmful if ingested, damaging to the eyes and irritating to the skin, and, to cause serious defects in developing embryos. Further, due to the C—H bonds and other functional groups of the photosensitizers disclosed by DeRosa et al, these materials are subject to self-destruction by the singlet oxygen that they produce.
There is clearly a need in the art for effective, quick, economically, and non-hazardous, environmentally friendly means to sterilize water and make it potable for human consumption; such as the use of photosensitized singlet oxygen—which are stable and not subject to destruction by singlet oxygen.